The present invention relates to a device for detecting the time of termination of opening operation of shutter blades of an electromagnetic programming shutter.
In an electromagnetic programming shutter in which the shutter blades serve also as a diaphragm aperture so that they may initiate closing operation before they are fully opened depending upon the scene brightness so as to limit the light quantity for achieving the proper exposure, it is required in order to obtain proper timing of operation of a stroboflash device that the time be detected at which the shutter blades initiates closing operation even before they are fully opened, i.e. the time at which the shutter blades attain the maximum aperture as the shutter blades initiate closing operation during the time they are being opened.
Heretofore, a device for detecting the time of termination of opening operation of the shutter blades of an electromagnetic shutter has been proposed in which electric contacts are secured to a shutter blade opening member and a shutter blade closing member, respectively, which are mechanically operated in coupled relationship thereto so that the then maximum aperture is detected. However, by such mechanically operated contacts, mechanical loads are given to these members so that the energy loss becomes too large to enable to use an electromagnetic shutter of a relatively small driving power.
Alternatively, another device has been proposed in which the timing of operating a stroboflash device is obtained by delaying a certain time period from the issuance of a shutter blade opening signal. In this case, however, an actually accurate timing can not be obtained because the actual time of attaining the maximum aperture is not detected.
In this connection, the present assignee filed a Japanese Utility Model Application which was publicly disclosed as Japanese Utility Model Public Discl. No. 54343/1979 in which a device for detecting the time of commencement of the opening operation or the time of attaining the maximum aperture of shutter blades of an electromagnetic shutter having a rotatable or stationary permanent magnet, comprises a stationary or movable electric coil electromagnetically coupled with the above rotatable or stationary permanent magnet, the rotatable permanent magnet or the movable electric coil being coupled with the shutter blades and being reciprocally rotated by a predetermined angle by supplying electric current to the coil in one direction for opening the shutter blades for a predetermined time period for the proper exposure depending upon the scene brightness and, thereafter, in the reversed direction for closing the shutter blades, an electromagnetic proximity or contactless switch being provided which is operated by utilizing the relative movement between a movable member moving in coupled relationship to the shutter blades and a stationary member thereby permitting the time of commencement of the opening operation or the time of attaining the maximum aperture of the shutter blades to be detected. In such a device, however, it is impossible to detect the operation of the shutter blades except for limited conditions under which the shutter blades reach the fully opened positions or they initiate an opening operation from the closed positions.
Therefore, in an electromagnetic programming shutter in which the shutter blades may initiate closing operation at various time even before they reach the fully opened positions depending upon the scene brightness, the time of termination of the opening operation of the shutter blades can not be detected thereby making it impossible to achieve proper operation of a stroboflash device used with such an electromagnetic programming shutter.